The present invention relates to a satellite surveillance and data link system and more particularly to a system for determining the range to mobiles, storing uploaded poll commands to mobiles until the poll is scheduled to be transmitted, and aquiring mobiles that request entry into the system through satellite on-board computing capability.
There is currently high-level commercial and government interest in the application of communication satellite technology to mobiles (e.g., aircraft, ships, and trucks). This technology has the advantage of almost unlimited coverage as compared to the restrictions of terrestrial line-of-sight limited communications and it eliminates the need for many ground-based facilities. There is also unused radio spectrum reserved for mobile-satellite communications. Satellites have been in successful operation for ship-to-shore communications for several years through a service provided by the international consortium, INMARSAT. Recently, the aviation community has rapidly begun to renew its interest for the use of satellites for air traffic control, airline operational control and public correspondence.
In known polling system methods using satellites for cooperative position determination, the satellite acts only as a repeater for ground initiated polls and replies from the mobile, and acts as a repeater for data messages. U.S. Pat. No. 4,359,733 discloses a GEOSTAR concept that utilizes satellites as repeaters in which ground based computers calculate ranges to mobiles.
Other known proposed systems also use the satellite solely as a repeater of the uplinked data from the ground, and rely upon centralized earth stations and terrestrial links for interconnection to control facilities such as air traffic control centers. On-board processing is a major theme of NASA's Advanced Communication Technology Satellite (ACTS) program and advanced military satellites. See, M. Kachnor, "Switchboards in the Sky," Microwave and RF, June, 1986, and M. E. Thimlar, et al., "Future Space-Based Computer Processors," Aerospace America, March 1984.
It is therefore an object of the present invention to provide a ranging and processing satellite system for cooperative mobile surveillance and data link service in which the satellites have on-board processing capability.
It is another object of the present invention to provide such a satellite system which can be directly accessed from multiple ground control facilities.
Yet another object of the invention is such a satellite-based system which is more efficient than previously known discrete address cooperative surveillance satellite systems.
Still another object of the invention is a satellite system including the use of cross-link communications between the satellites to provide data for on-board satellite position determination for on-board acquisition of mobiles into the system.
Yet another object of the invention is a system in which the on-board processing involves not only signal regeneration and beam switching capability, but also digital data processing of messages, for storage of poll commands, generation of polls to mobiles according to a schedule, storage of replies to polls, and formatting of messages.